Hollow, cellulose-type fibers are extensively used on a clinical basis in dialyzers for blood for the maintenance of patients who suffer end stage renal disease. Such dialyzers are also used for acute dialysis of patients for various other reasons. Despite the extensive, and successful use of such dialyzers, certain disadvantages and drawbacks remain.
During the manufacturing process, the fiber is formed as a continuous, hollow filament. The filament has an exterior peripheral surface that can be washed and purified during the manufacturing process. However, due to the continuous nature of the formed filament, the interior surface cannot be purified. Dialyzers are conventionally formed by bundling a plurality of coextending, hyperfiltrating, cellulose lumens or fibers bundled together in a supporting housing.
Prior to being used, such dialyzers are after flushed with selected solutions. One aspect of the flushing step is to minimize the extractables in the fibers before use.
From time to time it has been noted that a certain minor number of patients experience undesirable reactions during or after the dialysis process. These are apparently due to some unknown, extractable component of hollow cellulose-type ultrafiltration fibers, particularly those fibers which are made by the well known cupraammonium process.
Japanese Patent Publication No. 55-23620 of Toray Industries, Inc. entitled "Method for Sterilization of Dialysis Device", discloses a method of saturating the semipermeable membrane of a dialyzer with water, or an aqueous solution of a nontoxic, water-soluble substance such as sodium chloride or glycerin. The undried units are then sealed or packaged and subjected to sterilizing radiation. This is alleged to suppress radiation damage when the membranes are so sterilized.
Rowley et al. U.S. Pat. No. 3,592,672 discloses dry, stabilized rewettable semipermeable cellulose ester and ether membranes formed of sheet material. Rowley also discloses various methods of preparation of the sheet material. The sheet membrane may be washed, while water-wet, with a water miscible organic solvent to extract most of the water from the membrane, followed by contact of the membrane with a nonpolar hydrocarbon solvent, in which the water miscible organic solvent may contain a water soluble polyol such as glycerin. Treatment of such sheet materials is of necessity somewhat different from the treatment of continuous fiber materials. During the manufacturing process, all surfaces of the sheet-type materials are accessible for treatment or processing.
Manos U.S. Pat. No. 4,080,743 discloses a process for drying a water-wet membrane by contacting it with a solution of water miscible and water immiscible solvents and then removing the solution.
Bodner et al. U.S. Pat. No. 4,227,295 discloses a means for manufacture of artificial kidneys out of hollow fiber dialyzers, and provides a general background example of the extensive prior art of hollow fiber dialyzer manufacture.
Lipps U.S. Pat. No. 3,546,209 teaches a process for hydrolyzing cellulose ester fibers, followed by plasticizing the fibers while still wet with a water soluble, nonvolatile plasticizer such as glycerin and then drying the fibers before using them to manufacture a separatory cell. Pages 99 and 100 from a book by Scott, J., entitled Hollow Fibers: Manufacture and Applications, Park Ridge, N.J., Noyes Data Corporation (1981) discuss the Lipps patent cited above.
British Pat. No. 1,349,394 entitled "Preswelled Cellulose Films and Process Therefor" discloses methods of manufacturing sheet-type cellulose dialysis films. Among other steps, the British document discloses the known use of glycerin in the process of manufacturing the cellulose membrane.
It is thus desirable to process such dialyzer units so as to remove larger amounts of undesired extractable elements from the fibers, and then to reconstitute the fibers with their desired flexibility and softness. It is also desirable to provide enhanced protection to the hollow fibers against radiation damage which can take place in the event that the dialyser unit is radiation sterilized.